Photovoltaic devices, such as photocells, are an important energy source that has thus far remained underutilized for widespread energy production. Photocells generate electrical energy by converting photons from a light source into electricity (e.g., by freeing electron-hole pairs). Conventional photocells, however, typically provide a light-to-electricity conversion efficiency of only up to about 25 percent. Such a low conversion efficiency makes conventional photocells an undesirable option for most applications.
Attempts have been made to increase photovoltaic device energy conversion efficiency using nanotechnology, by incorporating nanowires, nanocrystals, etc. into active layers of the device. See, for example, U.S. Patent Application No. 2005/0009224 filed by Yang et al., entitled “Nanowire Array and Nanowire Solar Cells and Methods for Forming the Same” (wherein nanowire oxides are used in conjunction with a charge transport medium in optoelectronic devices); U.S. Patent Application No. 2005/0214967 filed by Scher et al., entitled “Nanostructure and Nanocomposite Based Compositions and Photovoltaic Devices” (wherein nanostructures, such as core-shell nanocrystals, are used in photovoltaic devices oriented horizontally along an electrode plane) and Kayes et al., Comparison of the Device Physics Principles of Planar and Radial p-n Junction Nanorod Solar Cells, 97 J. APPL. PHYS. 114302 (2005) (wherein radial p-n junction nanorod solar cells are described).
Efficiency improvements are, however, still needed to make photovoltaics a viable and practical energy source.